The spec nuke on its own deals way more dmg than the base line heat nuke, which also has some variance due to only having 22 points specced in light. Combined with the debuff, the raw dmg is higher, but you have to debuff your target first. If you are interested in playing in groups, you should consider going mana, as you are expected to debuff for the other casters. For solo and smallman I liked light spec.
One thing I've been wanting to test out is have two chanters, one mana spec for the heat debuff and one specced 50 enchantment for the last pet effectiveness buff. I wanted to see how hard a companion pet hit when buffed and with the target heat debuffed. Seems like it could be legit dps not sure if it would be more than 45light nuke+pet but my guess is the enchantment spec might come slightly out on top.
Pet nuked bears for like 350-400 with only heat debuff might be like 550-600 with pierce buff.
A light spec enchanter is more or less a light mentalist. You have a strong heat-based nuke, and a (less annoying) pet. Ment has crappy aoe dmg and ghetto heals (and even more ghetto mez). Chanter has some acceptable melee debuffs (keep in mind the phys-dmg insta is an interupt too) and delicious speed. If you aren't worried about any DS type pve - or even general fins/shreddrt farming - and you have someone to consistently lead the debuff train: a light chanter is workable.
Just a little unintentional
Remember the underhill zealot casts a heat dmg/debuff nuke 15% debuff. Add that to your spec heat nuke and you can do alot of single target ranged dmg ..although pet is not all that fast.